IRS2608DSPBF_1 Datasheet, PDF (11/26 Pages) International Rectifier – HALF-BRIDGE DRIVER

IRS2608DSPbF
Integrated Bootstrap Functionality
The IRS2608D embeds an integrated bootstrap FET that allows an alternative drive of the bootstrap supply for a wide
range of applications.
A bootstrap FET is connected between the floating supply V_B and V_CC (see Fig. 8).
Vcc
BootFet
Vb
Figure 8: Semplified BootFET connection
The bootstrap FET is suitable for most PWM modulation schemes, including trapezoidal control, and can be used
either in parallel with the external bootstrap network (diode+ resistor) or as a replacement of it. The use of the
integrated bootstrap as a replacement of the external bootstrap network may have some limitations in the following
situations:
• When the motor runs at a very low current (so that the negative phase voltage decay can be longer than
20us) and complementary PWM is not used.
• At a very high PWM duty cycle due to the bootstrap FET equivalent resistance (R_BS, see page 3).
The summary for the bootstrap state follows:
• Bootstrap turns-off (immediately) or stays off when at least one of the following conditions are met:
1- HO goes/is high
2- V_B goes/is high (> 1.1*V_CC)
• Bootstrap turns-on when:
1- LO is high (low side is on) AND V_B is low (< 1.1(V_CC))
2- LO and HO are low after a LIN transition from H to L (HB output is in tri-state) AND V_B goes low
(<1.1*V_CC) before a fixed time of 20us.
3- LO and HO are low after a HIN transition from H to L (HB output is in tri-state) AND V_B goes low
(<1.1(V_CC)) before a retriggerable time of 20us. In this case the time counter is kept in reset state until
VB goes high (>1.1V_CC). Please refer to the BootFET timing diagram for more details.
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